Onyx | Gemopedia

Onyx is the dark brown to black variety of agate, a cryptocrystalline quartz. Since ancient times onyx has afforded gem cutters and carvers an excellent source for carving cameos, intaglios and other jewelry creations. Inexpensive, abundant and available in large sizes, onyx is also a favored stone when fashioning cabochon gems and beads.
Alternate
Names
True Onyx, Arabic Onyx
Colors
Black, White In Alternating Layers

Onyx Classification

Common Name

Onyx

Species

Quartz

Variety

Chalcedony

Colors

Black, White In Alternating Layers

Alternate Names

True Onyx, Arabic Onyx

Gemstone Groups

Key Separations

RI, SG and appearance

Comments

Sometimes dyed and sold as black onyxSardonyx is different from onyx and is characterized by its carnelian or sard body color.

Onyx Optical Properties

Transparency

Semitransparent - Translucent

Refractive Index

1.535-1.539

Birefringence

0.004-0.004

Optic Character

Uniaxial

Optic Sign

Positive

Polariscope Reaction

Aggregate (AGG)

Fluorescence

SWUV: Inert
LWUV: Inert

CCF Reaction

Pleochroism

None

Dispersion

Strength: none

Comments

Onyx Chemistry & Crystallography

Chemical Name

silicon dioxide (aka silica)

Chemical Formula

SiO2

Synthesis

Crystal System

Trigonal

Classification

Silicate

Nature

Natural

Crystallinity

Polycrystalline

Comments

Onyx Characteristic Physical Properties

Hardness

6.5-7

Streak

White

Specific Gravity

2.55-2.7 Typical:2.6

Toughness

Excellent

Inclusions

Onyx will have straight parallel layers of different colors.

Luster

Vitreous

Stability

Good

Fracture

Conchoidal, Granular

Cleavage

None

Comments

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